NatWest customers have been hit by more internet banking issues after a cyber-attack knocked the bank's website down for an hour.

No accounts were hacked and no customer information was at risk during the attack, which prevented NatWest customers from accessing online services from around midday on 6 December. The website has been restored and services returned to normal.

It comes just days after an unrelated IT systems glitch hit the Royal Bank of Scotland Group, which owns NatWest, and prevented many customers from accessing accounts or making payments.

"Due to a surge in internet traffic deliberately directed at the NatWest website, customers experienced difficulties accessing some of our customer web sites today," said a spokeswoman for RBS.

"This deliberate surge of traffic is commonly known as a distributed denial of service (DDoS) attack.

"We have taken the appropriate action to restore the affected web sites. At no time was there any risk to customers. We apologise for the inconvenience caused."

A DDoS attack seeks to disrupt websites and other computer systems by flooding the targeted organisations' networks with computer traffic.

It is much harder to deflect than a regular Denial-of-Service (DoS) attack as there is simply no single attacker to defend from.

A regular DoS attack targets and is carried out by one computer and one internet connection, which overwhelms just a single server with packets of data.

According to the International Organization of Securities Commissions' (IOSCO) research department and the World Federation of Exchanges Office (WFEF), a variety of studies estimate that global total for all cyber-crime costs range between $388bn (£256bn, €296bn) to $1tn.

RBS received a taxpayer-funded £45bn bailout in 2008, leaving it 81% owned by the government.

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